Method and apparatus for the regulation of the warp let-off a weaving machine

ABSTRACT

A method and an apparatus for the regulation of the warp let-off of a weaving machine is proposed, in that a desired speed of rotation (S D ) is predetermined for a warp beam ( 2 ), in that a warp tension (K) of the warp threads ( 3 ) which are given off by the warp beam ( 2 ) is determined, in that the warp tension (K) is weighted with a weighting function (G) and in this manner a weighted warp tension (K G ) is determined, in that a corrected desired speed of rotation (S DK ) is determined from the values of the desired speed of rotation (S D ) and the weighted warp tension (K), and in that the speed of rotation of the warp beam ( 2 ) is controlled in dependence on the corrected desired speed of rotation (S DK ).

[0001] The invention relates to a method for the regulation of the warp let-off of a weaving machine in accordance with the preamble of claim 1. The invention also refers to an apparatus for carrying out the method in accordance with the preamble of claim 10.

[0002] The patent specification U.S. Pat. No. 4,942,908 discloses a regulation apparatus for a weaving machine which, for influencing the warp thread tension, correspondingly varies the speed of rotation of the warp beam. This regulation apparatus is operated in two fundamentally different operating modes. In a first operating mode a fixed speed of rotation with which the warp beam is rotated is predetermined independently of the warp thread tension. In a second operating mode the tension of the warp threads is measured with a sensor and the speed of rotation of the warp beam is regulated in such a manner that the tension of the warp threads corresponds to a predetermined value. This known regulation apparatus enables the cloth density to be influenced in that the tension of the warp threads is varied correspondingly. The tension of the warp threads influences the way they are worked into the developing cloth and thus also influences the cloth density. The nature of the tension regulation in the warp threads is therefore of central importance in order to produce a cloth of uniform, reproducible quality.

[0003] Disadvantageous in the known regulation is the fact that the cloth which is produced has a reduced quality, for example if the constitution of the woven yarn, for example the E-module, is subject to fluctuations, or when differing weaves are woven.

[0004] The object of the present invention is to propose a method for the regulation of the warp let-off of a weaving machine which enables a higher cloth quality to be produced.

[0005] This object is satisfied by a method having the features of claim 1. Subordinate claims 2 to 9 relate to further, advantageous method steps. The object is furthermore satisfied by an apparatus having the features of claim 10.

[0006] The object is satisfied in particular by a method for the regulation of the warp let-off of a weaving machine, in that a desired speed of rotation S_(D) is predetermined for a warp beam, in that a warp tension K of the warp threads which are given off by the warp beam is determined, in that the warp tension K is weighted with a weighting function G and in this manner a weighted warp tension K_(G) is determined, in that a corrected desired speed of rotation S_(DK) is determined from the values of the desired speed of rotation S_(D) and the weighted warp tension K_(G) and in that the speed of rotation of the warp beam is controlled in dependence on the corrected desired speed of rotation S_(DK).

[0007] An advantage of the method in accordance with the invention is to be seen in that no weaving phases arise within which the warp tension is not defined. The warp let-off of the weaving machine, or the speed of rotation of the warp beam respectively, is determined both by a predetermined desired speed of rotation and by the measured warp tension of the warp threads.

[0008] In an advantageous embodiment the warp tension is weighted with a weighting function, with the weighting factor being settable, so that it can be determined to what extent the warp tension should influence the speed of rotation of the warp beam. The method in accordance with the invention is usually operated in such a manner that the speed of rotation of the warp beam depends both on the predetermined desired speed of rotation and on the measured warp tension.

[0009] Through a corresponding choice of the value of the weighting factor, however, the following two special cases can arise.

[0010] If the weighting factor is set to zero, then the warp tension no longer has an effect on the speed of rotation of the warp beam. In this the speed of rotation is determined solely by the predetermined desired speed of rotation. A regulation of the warp let-off of this kind is also designated as a “positive warp supply system” or as a “positive system”. This positive system is preferably set in such a manner that a constant warp thread length per weaving cycle is supplied, independently of the tension values arising in the warp threads.

[0011] If the weighting factor is set to infinity, then the value of the predetermined desired speed of rotation no longer has an effect on the speed of rotation of the warp beam. A regulation of the warp let-off of this kind is also designated as a “negative warp supply system” or as a “negative system”. This negative system has the property that the warp threads are supplied in such a manner that the tension of the warp threads has a predetermined value. The warp thread length which is supplied per weaving cycle is thus dependent on the tension of the warp threads.

[0012] A regulation apparatus for the negative system can be built up in such a manner that the warp tension is measured and is compared in a warp tension regulator with a desired value. The warp tension regulator forms as its output signal a desired speed of rotation which is supplied to a speed of rotation regulator which is placed afterwards in order to control the speed of rotation of the warp beam in accordance with the desired speed of rotation.

[0013] A regulation in accordance with the positive system has the disadvantage that the warp thread tension is subject to large fluctuations, caused for example by varying yarn constitution and/or varying weave, so that the cloth which is manufactured with this regulation method can have a disadvantageous cloth appearance.

[0014] A regulation in accordance with the negative system likewise has the disadvantage that a cloth with a disadvantageous cloth appearance is produced, as a result for example of varying yarn constitution and/or varying weave.

[0015] A substantial advantage of the method in accordance with the invention is to be seen in that the working in of the warp is subject to slight fluctuations. The working in of the warp is understood to mean the quotient of the warp thread length which is consumed and the cloth length which is produced. The working in of the warp depends among other things on the warp thread tension or on the length of warp thread which is given off by the warp beam. As a rule the quantitative relationship between the working in of the warp and the warp tension is not known during the weaving, which has the result that in a regulation in accordance with the negative system the desired value for the warp tension in order to achieve a specific working in of the warp can not be precisely predetermined. In addition to the running properties of the weaving process, which determined the warp tension and thereby the working in of the warp, the working in of the warp is also influenced by specific article factors such as weft density or weave. Therefore in spite of an exact regulation of the warp tension it is not ensured that the cloth which is produced has the required working in of the warp, or, respectively, that the cloth has a good dimensional stability or a uniform cloth weight.

[0016] The method in accordance with the invention enables a regulation of the warp let-off in accordance with both a positive and a negative system. Of central importance, however, is that the method in accordance with the invention enable a regulation in a mixed form of a positive system and a negative system. The respective components of the positive system and the negative system in the regulation method can in addition be set via the values of the weighting function G.

[0017] The method in accordance with the invention enables a cloth of higher quality to be manufactured, in particular a cloth with a balanced working in of the warp, which means a cloth with a uniform cloth weight.

[0018] In an advantageous further development of the method in accordance with the invention both the warp thread length which is given off by the warp beam and the cloth length which is produced are measured in order to determine from these data a value for the working in of the warp. In a further, advantageous method the weighting function is varied in dependence on the value for the working in of the warp in such a way that a cloth with a predetermined desired value for the working in of the warp is manufactured.

[0019] In the following the invention will be explained with reference to a plurality of exemplary embodiments. Shown are:

[0020]FIG. 1 a first exemplary embodiment of a regulation apparatus;

[0021]FIG. 2 a first characteristic curve, which represents the relationship between the warp tension and the corrected desired speed of rotation;

[0022]FIG. 3 a second exemplary embodiment of a regulation apparatus;

[0023]FIG. 4 a second characteristic curve with a corrected desired speed of rotation;

[0024]FIG. 5 a third characteristic curve with a corrected desired speed of rotation;

[0025]FIG. 6 schematically, a weaving machine with a cloth beam.

[0026]FIG. 1 shows a warp beam 2 which is driven by a motor 4 and which supplies warp threads 3 to the weaving machine. The actual speed of rotation I_(D) of the warp beam 2 is measured by a sensor 7. The warp tension K of the warp threads 3 is measured by a sensor 5. The regulation apparatus 1 measures the warp tension K, weights the latter in a transfer member 6 with a weighting function G and conducts the weighted warp tension K_(G) to an adding element. A corrected desired speed of rotation S_(DK) is calculated from a predetermined desired speed of rotation S_(D) and the weighted warp tension K_(G) through addition. This corrected desired speed of rotation S_(DK) serves an underlying control circuit as a guiding parameter. The regulation apparatus for the speed of rotation 8 of the underlying control circuit is advantageously designed as a PID regulator, so that the error signal F of the underlying control circuit tends to zero and the speed of rotation of the warp beam 2 is thereby controlled via the motor 4 and the speed of rotation sensor 7 in such a manner that the speed of rotation of the warp beam 2 corresponds substantially to the corrected desired speed of rotation S_(DK).

[0027] The value of the weighting function G can be entered manually in the transfer member 6. It can however also prove advantageous to supply the value of the weighting function G electrically, for example via a line 11, to the transfer member 6.

[0028]FIG. 6 shows schematically a weaving machine having a warp beam 2 with warp threads 3 which is driven by a motor 4 and a cloth beam 12 with cloth 13 which is driven by a motor 14. By means of speed of rotation sensors 7, 15 the speed of rotation of the warp beam 2 and of the cloth beam 12 is measured by the higher level regulation apparatus 16. In addition the latter measures the warp tension K with a tension sensor 5. The higher level regulation apparatus 16 produces, for example in dependence on the diameter of the warp thread winding which is present on the warp beam 2, a corresponding desired speed of rotation S_(D) for the warp beam 2. This desired speed of rotation S_(D) is supplied to the regulation apparatus 1.

[0029] The method in accordance with the invention for the regulation of the warp let-off proceeds now in such a manner that a desired speed of rotation S_(D) is specified for the warp beam 2 by the higher level regulation apparatus 16, that the warp tension K of the warp threads 3 which are given off by the warp beam 2 is measured, that the warp tension K is weighted by a weighting function G and a weighted warp tension K_(G) is determined in this manner, that a corrected desired speed of rotation S_(DK) is determined from the values of the desired speed of rotation S_(D) and the weighted warp tension K_(G), and that the warp beam 2 is controlled with the corrected desired speed of rotation S_(DK).

[0030]FIG. 2 shows in a first characteristic curve K1 a linear relationship between the warp tension K and the corrected desired speed of rotation S_(DK). The formula G=α(K−Ko) holds for the weighting function G. The factor α of the weighting function determines the slope of the characteristic curve K1. The factor Ko is chosen in such a manner that the desired speed of rotation S_(D), as illustrated in FIG. 2, comes to lie at a preferred warp tension Ko. The regulation of the warp let-off using the first characteristic curve K1, which is shown in FIG. 2, proceeds as follows: As long as the warp tension K maintains the value Ko, the value of the corrected desired speed of rotation S_(DK) corresponds to the value of the desired speed of rotation S_(D). As soon as the warp tension K increases, the value of the corrected desired speed of rotation S_(DK) also increases corresponding to the plot of the first characteristic curve K1, so that the warp beam 2, as is illustrated at point K₁₃, is operated with a corrected desired speed of rotation S_(DK) which is increased with respect to the desired speed of rotation S_(D). In this region, which is designated by V_(E), the corrected desired speed of rotation S_(DK) has a higher value than the desired speed of rotation S_(D), which is also designated as an overfeed V_(E). As soon as the warp tension K drops below the value Ko, the value of the corrected desired speed of rotation S_(DK) decreases corresponding to the plot of the first characteristic curve K1, so that the warp beam 2, as is illustrated at point K₁₄, is operated with a corrected desired speed of rotation S_(DK) which is reduced with respect to the desired speed of rotation S_(D). In this region, which is designated by N_(E), the corrected desired speed of rotation S_(DK) has a lower value than the desired speed of rotation S_(D), which is also designated as an underfeed N_(E). The behaviour which is illustrated in FIG. 2 imparts a stable behaviour to the regulation of the warp let-off. If for example as a result of a variation of the warp thread properties an increase of the warp tension K arises, then the corrected desired speed of rotation S_(DK) and thereby also the speed of rotation of the warp beam 2 is increased correspondingly, so that the warp tension K is again reduced, and the regulatory system stabilises at a new working point.

[0031] The regulation characteristic curve of the method in accordance with the invention can be influenced by a plurality of measures. The value of the corrected desired speed of rotation S_(DK) can be increased or reduced independently of the value of the warp tension in order to vary the regulation characteristic curve. In addition it is usual for the desired speed of rotation S_(D) to be varied by the higher level regulation apparatus 16 during the operation of the weaving machine, for example in dependence on the amount of the warp threads 3 which are present on the warp ware beam 2.

[0032] The regulation characteristic curve can also be varied through a variation of the weighting function G. For example, the factor α can be increased/decreased so that the curve K1 has a greater/lesser slope α. Too large a value for the factor α leads substantially to a negative warp infeed system, in that the warp tension K is regulated independently of the desired speed of rotation S_(D). Too small a value for the factor α leads substantially to a positive warp infeed system, in that the corrected desired speed of rotation S_(DK) is substantially independent of the warp tension K. The regulation of the warp let-off in accordance with the invention thus unites the properties of the positive and the negative warp infeed systems. The ideal value for the factor α depends on the most diverse aspects, such as weaving conditions, yarn properties or weave. The factor α is preferably set for a specific article to be woven in each case. Thus, for example, a weaving process can be started in that a large value is set for the factor α at the beginning. The effect on the cloth which is produced is observed, the working in of the warp is measured and then the factor α is possibly changed again until the ideal setting for this factor has been found. For yarns with a high modulus of elasticity the factor α should have a small value, since otherwise small variations in the warp tension would cause a large variation of the warp infeed. Correspondingly, a factor α with a large value is advantageous for yarns with a low elasticity module.

[0033] The weighting function G can be defined in a large number of possible functions. In order to be able to dynamically influence warp tension variations it can prove advantageous to additionally define the weighting function G as a function of time. A weighting function of this kind could for example be defined as G=α(1−e^(−bt)). As a result of the exponential function the weighted warp tension K_(G) is also dependent on the time t, in addition to the value of the warp tension K and the value of the factor α as a function of the time t.

[0034] In addition to the regulation apparatus in accordance with FIG. 1 the second exemplary embodiment of a regulation apparatus 1 which is illustrated in FIG. 3 also has a threshold value switch 9 as well as two electrical change-over switches 10 a, 10 b, which are actuated by the relay 10. The warp tension K is supplied to the threshold value switch 9, which compares the value of the warp tension K with a lower warp tension K_(SU) and an upper warp tension K_(SO). As long as the value of the warp tension K lies between the values K_(SO) and K_(SU), the electrical change-over switches 10 a, 10 b assume the position illustrated in FIG. 3. A soon as the value of the warp tension K is greater or less than the values K_(SO) or K_(SU), the threshold value switch 9 produces a switching signal, which actuates the electrical switching device 10 and changes the position of the electrical change-over switches 10 a, 10 b. The first change-over switch 10 a thereby conducts a desired warp tension S_(K) to the electrical line 17. The second change-over switch 10 b separates the value of the desired speed of rotation S_(D) from the regulation apparatus 1. Through this the regulation apparatus 1 operates as a pure warp tension regulator, in that the desired warp tension S_(K) is preset for the regulation apparatus 1. In this it should be observed that the value of the desired warp tension S_(K) must lie above or below the value K_(SO), K_(SU).

[0035] During the triggering of the threshold value switch 9 an alarm can additionally be triggered in order to alert a supervisory person. The threshold value switch 9 can have a manual input Man in order to be able to reset the threshold value switch 9 back into the operating mode which is illustrated in FIG. 3.

[0036] The regulation apparatus 1 in accordance with the invention is also suitable for the operation of a weaving machine with a first and a second warp beam 2. In this each of the two warp beams 2 is driven by a separate motor 4, with the arrangement with regulation apparatus 1 and sensors 5, 7 for controlling the motor 4 which is illustrated in FIG. 1 being provided for each warp beam 2. FIG. 4 shows the characteristic curve K₁ of the first regulation apparatus 1, which is used for the first warp beam 2. The characteristic curve K₁ has a slope α₁. FIG. 5 shows the characteristic curve K₂ of the second regulation apparatus 1, which is used for the second warp beam 2. This characteristic curve K₂ can have a different slope α₂. These different slopes α₁, α₂ are advantageous in particular when the warp threads 3 of the individual warp beams 2 have different textile properties, such as a different elasticity. One of the warp beams 2 is advantageously chosen as a master system and the other warp beam 2 as a slave system, the desired speed of rotation S_(D) of which is predetermined by the master system. In the illustrated exemplary embodiment the first warp beam 2 is operated as the master system in accordance with the characteristic curve K₁ which is illustrated in FIG. 4, whereas the second warp beam 2 is operated as the slave system in accordance with the characteristic curve K₂ which is illustrated in FIG. 5. The first warp beam 2 is operated, as already described with FIG. 2, in such a manner that a desired speed of rotation S_(D) is predetermined, which yields the point K₁₁ on the characteristic curve K₁. As a result of the warp tension of the warp threads which are given off from the first warp beam 2, the regulation apparatus 1 produces via the point K₂₂ the corrected desired speed of rotation S_(DK) with which the first warp beam 2 is rotated. This corrected desired speed of rotation S_(DK) is specified as the desired speed of rotation S_(D) to the slave system, which controls the second warp beam 2. The warp tension of the second warp beam 2 can vary independently of the first warp beam 2. The regulation apparatus 1 of the second warp beam 2 produces, as shown in FIG. 5, the corrected desired speed of rotation S_(DK) with which the second warp beam 2 is rotated as a result of the measured warp tension and taking into account the characteristic curve K₂. This kind of regulation has the result that the two warp beams 2, which have warp threads with different properties, can have different warp tension values and different speeds of rotation. This regulation with a master system and a slave system enables a uniform working in of the warp even in the event of warp threads with different properties.

[0037]FIG. 8 shows a part of a cloth 13 consisting of warp threads 3 and weft threads 18. The cloth 13 has a 1/1 weave. For this weave the working in of the warp C is defined as C=(L1−L2)/L2, with the worked in warp thread length being designated by L1 and the cloth length which is produced being designated by L2.

[0038]FIG. 7 shows a regulation apparatus 19 to which the measured value for the worked in warp thread length L1 and the measured value for the cloth length L2 which is produced are supplied, so that the regulation apparatus 19, as illustrated, is able to determine the current value of the working in of the warp C, which is designated as the actual working in of the warp (C_(IST)). This value is compared with a predetermined desired working in of the warp (C_(SOLL)) in that the difference of these two values is formed and this difference signal is supplied to a PI regulator 20. This regulator 20 produces a signal for correcting the specification of the factor α in the weighting function G, which is supplied via the line 11, as illustrated in FIG. 1, for example to the transfer member 6. The cloth length L2 which is produced can for example be determined with the help of the sensor 15, which measures the speed of rotation of the cloth beam 2.

[0039] It can also prove advantageous to smooth the values which are measured by the tension sensor 5 and/or the speed of rotation sensor 7, or, respectively, to form an average value from the measured values, before these values are supplied to a following unit.

[0040] The method in accordance with the invention for the regulation of the warp let-off is suitable for the most diverse types of weaving machine, for example for projectile weaving machines, for air jet weaving machines, for multiple phase weaving machines or for rapier weaving machines. 

1. Method for the regulation of the warp let-off of a weaving machine, in that a desired speed of rotation (S_(D)) is predetermined for a warp beam (2), in that a warp tension (K) of the warp threads (3) which are given off by the warp beam (2) is determined, in that the warp tension (K) is weighted with a weighting function (G) and in this manner a weighted warp tension (K_(G)) is determined, in that a corrected desired speed of rotation (S_(DK)) is determined from the values of the desired speed of rotation (S_(D)) and the weighted warp tension (K), and in that the speed of rotation of the warp beam (2) is controlled in dependence on the corrected desired speed of rotation (S_(DK)).
 2. Method in accordance with claim 1, characterized in that the added values of the desired speed of rotation (S_(D)) and the weighted warp tension (K_(G)) yield the corrected desired speed of rotation (S_(DK)).
 3. Method in accordance with any one of the preceding claims, characterized in that the weighting function (G) has only a factor α, by which the warp tension (K) is multiplied.
 4. Method in accordance with any one of the preceding claims, characterized in that the tension of the warp threads (3) is varied in that the value for the desired speed of rotation (S_(D)) and/or the value of the weighting function (G), in particular the value of the factor α, is varied.
 5. Method in accordance with any one of the preceding claims, characterized in that the weaving machine comprises a first and a second warp beam (2) which can be controlled separately; and in that for each warp beam (2) a separate, corrected desired speed of rotation (S_(DK)) is determined; and in that the speed of rotation of each warp beam (2) is controlled in accordance with the separate, corrected desired speed of rotation (S_(DK)).
 6. Method in accordance with claim 5, characterized in that the separate, corrected desired speed of rotation (S_(DK)) of the first warp beam (2) is used as the value for the desired speed of rotation (S_(D)) of the second warp beam (2).
 7. Method in accordance with any one of the preceding claims, characterized in that when the warp tension (K) exceeds or drops below a predetermined warp tension value (K_(SO), K_(SU)) the corrected desired speed of rotation (S_(DK)) is produced without using a value for the desired speed of rotation (S_(D)); in that a difference value is formed between the warp tension (K) and a predetermined desired warp tension (S_(K)) and the difference value which is weighted with the weighting function (G) forms the corrected desired speed of rotation (S_(DK)) by means of which the speed of rotation of the warp beam (2) is controlled.
 8. Method in accordance with any one of the preceding claims, characterized in that the warp thread length (L1) which is given off from the warp beam (2) and the cloth length (L2) which is produced are measured and the actual working in of the warp (C_(IST)) is determined therefrom.
 9. Method in accordance with claim 8, characterized in that the weighting function (G), in particular the factor α, is varied in dependence on the actual working in of the warp (C_(IST)).
 10. Apparatus for carrying out the method in accordance with any one of the preceding claims, comprising a tension sensor (5) for measuring the tension of the warp threads (3), comprising a speed of rotation sensor (7) for measuring the speed of rotation of the warp beam (2), comprising a regulation apparatus (1) which is connected in a signal-conducting manner to the tension sensor (5) and to the speed of rotation sensor (7), as well as comprising a motor (4) which drives the warp beam (2) and which is connected in a signal-conducting manner to the regulation apparatus (1). 